Vehicle suspension system

Abstract

A vehicle suspension system includes a suspension unit comprising a hydraulic actuator of variable displacement connected to the chassis or body of the vehicle and a wheel and hub assembly of the vehicle and a control device for varying the displacement of the actuator in response to signals received from transducers on the vehicle to control the vehicle suspension. The suspension unit further comprises a displacement detector device to detect when the actuator displacement approaches a desired maximum/minimum value and a device to modify the velocity demand signal which operates in response to the control signal generated by the displacement detector device to bring the extension/contraction of the actuator gradually to a stop as the desired maximum/minimum value is reached.

What is claimed is: 
     
       1. A suspension unit of a wheeled vehicle comprising: a hydraulic actuator of which the displacement is variable by control of the flow of hydraulic fluid to at least one side of the piston and cylinder thereof;   means to connect the actuator to the body and a wheel hub of the vehicle so that variation of the displacement of the actuator controls the height of the body above the wheel hub;   transducers on the vehicle which generate signals, each transducer providing a signal indicative of at least one of force applied to the body by the actuator, longitudinal acceleration of the vehicle, lateral acceleration of the vehicle, speed of vehicle and yaw rate of the vehicle;   control means to control the flow of fluid to and from the actuator, in response to the signals generated by the transducers, to control the vehicle suspension, said control means comprising a processor which generates a velocity demand signal which corresponds to a velocity required of the actuator and a hydraulic control circuit controlled by the velocity demand signal;   displacement detector means to detect when the actuator displacement approaches a desired maximum/minimum value and to generate a control signal when the actuator displacement approaches the desired maximum/minimum value; and   means to modify the velocity demand signal which operates in response to the control signal generated by the displacement detector means to being the extension/contraction of the actuator gradually to a stop as the desired maximum/minimum value is reached.   
     
     
       2. A suspension unit as claim in claim 1 wherein the actuator has a mid-position of displacement and the means to modify the velocity demand signal determines whether the velocity demand signal requires displacement of the actuator toward or away from the mid-position and only modifies the velocity demand signal when the velocity demand signal requires displacement of the actuator away from the mid-position. 
     
     
       3. A suspension unit as claimed in claim 1 wherein said means to modify the velocity demand signal comprises means to weight the velocity demand signal selectively as a function of at least one of the displacement of the actuator and the value of the velocity demand signal. 
     
     
       4. A suspension unit as claimed in claim 1 is included in an active suspension system for a vehicle having a plurality of wheel hubs and a body comprising a plurality of the suspension units with the actuator of each suspension unit connected between each wheel hub of the vehicle and the body.